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5 Forest Succession, Fire, and Landscape Dynamics
Pages 108-121

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From page 108...
... ∑ Logging activities represent a reasonable surrogate for natural disturbances. This chapter presents a conceptual framework for understanding the factors responsible for varying patterns of natural disturbance and the successional processes that derive from them.
From page 109...
... , and the change in understanding of succession has major implications for the management of Pacific Northwest forests. We now recognize that fire and other disturbance processes operate over a wide range of spatial scales and were indeed an integral part of the primeval landscapes.
From page 110...
... For example, as forests develop, changes in structure, species composition, and the accumulation of organic matter alter fire susceptibility. Those changes may increase the likelihood of fire or other disturbances, as happens with the ingrowth of shade-tolerant firs and accumulation of woody fuels In Eastside ponderosa pine forests.
From page 111...
... Where the red alder cover is particularly dense, seedling establishment of Douglas-fir may be inhibited. Where seedling establishment is sparse and initial tree density or stocking generally low (e.g., many ponderosa pine forests)
From page 112...
... In over situations, patterns of fuel accumulation and frequency of ignition are such that the process is interrupted before reaching the later stages. Shade-tolerant trees may not become successfully established in forests with frequent ground fires (as in ponderosa pine and Douglas-fir on drier sites)
From page 113...
... Presert/ement Fire Regimes and Successiona/ Change Before IS50, infrequent, severe fires ("stand-replacement fires") with a highly variable return interval of more than 100 years were common In the western hemlock/Douglas-fir forests, Pacific silver fir forests, and subalpine forests (Agee 1993~.
From page 114...
... In northern California and southern Oregon, where the coastal redwood is important, fire regimes are much more variable. Return times of 400-500 years can be the norm in moist areas, and more frequent surface fires (every 50 years)
From page 115...
... Extensive stands of lodgepole pine characterize higher-elevation forests, while a complex of Douglas-fir and ponderosa pine forests dominate at lower elevations. Montana and Idaho forests dominated by Douglas-fir generally have longer fire intervals than ponderosa pine forests.
From page 116...
... Foresters have long recognized Over the past century, human the differences in activities in the Pacific Northwest have susceptibility to altered fire regimes enormously. fire of different age classes of forests.
From page 117...
... The combination of successional ingrowth associated with fire exclusion ancE the development of more densely stocked stands after logging has increased the likelihood of extensive surface fires in the region. That condition probably extends to higher-elevation forests as wed (Perry 1 988a)
From page 118...
... Patterns of ecosystem response (e.g., nutrient transformations, changes in species composition, and accumulation of flammable fuels) vary considerably among fire and silvicultural regimes as a function of predisturbance history, site conditions, disturbance characteristics, end postdisturbance environment.
From page 119...
... Logging has been proposed as a possible surrogate for fire in reducing fuel accumulations with the added benefit of economic return (Agee 1993) , but logging or clearcutting do not necessarily reduce flammable fuels.
From page 120...
... It is conventional wisdom that the loss of nutrient capital owing to forest cubing is considerably greater than that due to fire, and it seems obvious that clearcu~ng coupled with slash burning results in large nutrient losses. However, carefully controlled studies comparing nutrient budgets among different fire regimes or cutting treatments have not been conducted.
From page 121...
... Bio/ogica/ Diversity Given the close tie between the life history of some species and fire (e.g., serotinous cones in lodgepole pine and heat-stimulated germination in some shrubs) the responses of many species to fire differ from their responses to cutting.


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